Elizabeth



- H.-E. DUNHAM- INTERNAL COMBUSTION ENGINE Filed May 29, 1929 4 Sheets-Sheet 1 Oct. 12 1926.

H. E DUNHAM INTERNAL COMBUSTI 0N ENGINE Filed May 29, 1920 4 Sheets-Sheet 5 Oct. 12 1926.

Filed May 29 1920 4 sheets-Sheet 4 Gum M Patented Oct. 12, 1926.

UNITED stare-s PATENT ()FFICE.

HnnMon n. DUNEEAM, on SEATTLE, WASHINGTON; ELIZABETH; DUNHAM EXE U- ran: on SAID HERMON DUNHAM, nncnasnn INTERNAL-COMBUSTION ENGINE.

application filed May 29,

a gases will be effective in driving the corre sponding pistons in opposite directions, sub- 7 stantiallycounterbalancing the vertical components of the several forces on the crank shaft, so that the latt'erpractically floats in its bearings, and utilizing practically all of the heat units developed by {the combustion of the fuel and converting the sameinto ef- 'fective work, the expansion of the gases preferably being'carried .to a point below that of atmospheric pressure, so that the ultimate exhaust products are substantially devoid of force andheat. The novel mode of and mechanism for distributing the 'ex-' plosivecharges to multiple cylinders of the engine also admits of the engine, and the vehicle or other machine operated thereby being started from a position of rest by means of air which has been-compressed by the normal operation of the engine, or by the engine operating as a pump when it is desired to brake the engine and the apparatus operated thereby, so that the engine may be started and stopped very quickly and smoothly, without any shifting of gears,

or operating clutches or hand or power brakes, andwithout calling into play the I usually complicated and expensive electric starting gear. The foregoing, and other.

characteristic features and advantages of the novel method and apparatus involved in the invention will appear .more fully in the annexed specification and claims, which .are predicated upon the accompanying drawings exemplifying the invention'as applied to a six cylinder'engine of the fourf cycle type. I In the drawings:-

Fig. 1 s an end elevation ofthe engine with certain ofthe elements shown in cross section. v I

Fig. 2 is a front elevation.

Fig. 3 is a vertical transverse section on line 3-3 of Fig. 2.

4 is a partial section on line of Fig 2 1920. Serial NO. 385,304.

Fig. 5 is a sim of Fig.2. n Fig. 6 is a section, on line 6-6 of Fig. 3, of the piston rod guide.

Fig.7 is a detail view showing the means for operating the air inlet valves.

- Fig. 8 is a partial longitudinalsection of the cam roller forming part of the apparatus illustratedin Fig. 7.

Fig. 9 is 'a skeleton diagram of the engine and its operating devices.

Fig. 10 is a similar diagram in end elevation.

Figs. 11, 12 and 13 are diagrammatic views of the by-pass valve, the exhaust valve, and the fuel inlet valve. and their operating cams, respectively. I

Referring to the drawings 1 indicates the main cylinder casting, which is preferably formed as a single casting, and comprising six cylinders numbered 1 to, 6, inclusive, as indicated in Fig. 9, which cylinder casting is provided with a top or cover2, bolted to the member 1 and provided with firing chambers and valve chambers corresponding to thercspective cylindersf The cylinder block is connected by suitable base flanges to the top of'the frame 7 which, with th lower base iniember 8, constitutes the housing for the crank shaft and the camshafts'for operating the several valves, as is usual in engines of thisgeneral type. Each cylinder includes anupper section 3 and a lower section 8, which latter is of the respective sections adapted to receive the ends 5 and 6 of a differential :piston 4, the cylinder engaging walls of the pistons beingprovided with the usual form of packing rings. The lower piston head 6 is formed by an annular extensionof the piston bodyto provide a shoulder which serves to compress air in the cylinder space trav ersed by the lower end of'the piston, in sub-' stantially the same manner and for the same purpose as described in my Patent No. 1,1Q6,l94l, dated August 4, 1914. Each piston l isconnected by means of a piston rod lO and a connecting rod 10 to a suitable crankshaft 9 journalled in the ends larger diameter than ,the upper section,

to brace and support the piston rod against lateral thrusts. It will be understood that the arrangement and disposition of the several cranks on the shaft 9 may be designed to meet any particular order or sequence of operation of the several cylinders and pistons, and in the particular exemplification of the apparatus, the cranks are so disposed that the several cylinders are fired in the followingorder:No. :1, No. a, No. 2, h o. 6, No. 3, and No. 5, so that one cylinder fires forevery 120 rotation of the crank shaft. Each cylinder is connected near its top with a fuel inlet pipe 15, which delivers the explosive charge from a suitable manifold, not shown, which is connected with a carburetor or other suit-able charge-forming device, said fuel inlet pipe communicating with aport 15 which is controlled by a valve 16 normally held to its seat by a spring 18' on rod 17, which latter is guided in suitable openings formed in the engine castings, as illustrated in Fig. 3. The lower end of each inlet valve stem, is in cooperative engagement with a corresponding cam 20, the several cams being fixed at proper intervals upon a loi'igitudinal shaft 19 journalled in the ends of the casing 7.

Upon the end of the shaft 19 is secured a sprocket wheel 22, driven by a chain 23 which, in turn, is driven from a sprocket,

gear 21. on the end of the crank shaft 9, said chain also engaging a sprocket wheel on the end of a second cam shaft 26,-

the ratio between the sprocket gear 21 and the sprocket wheels on the cam shaft-s 19 and .26 being such that two revolutions of the crank shaft 9 produce a single revolution of each of the shafts 19 and 26.

The cam shaft 26 is o-urnalled in the casing 7 on the opposite side of the latter from the cam shaft 19 and, as indicated, is driven atone-half the speed of the crank shaft. Fixed at regular intervals on said shaft 26 is a series of cams 27, each having diametrically oppositely disposed raised portions approximately 90 in extent, and

which serve to open the exhaustvalves associated with the several cylinders and hold them open through approximately 180 of the crank shaft travel and in this particuthe entire downward lar case, during strokes of the pistons.

It will be noted that the lower end of each cylinder is formed in the upper face of the frame or casing 7, as illustrated in Fig. 3, and communicates with a valve chamber 31 in which operates the exhaust valve 29, which serves to open and close communication between the exhaust manifold 32, bolted to the side of the casing, through an exhaust duct 33, said valve being provi led with a stem 28 operating in suitable guides. the lower end of the stem cooperating with the corresponding cam 27 .31 as illustrated in'Fig. 3.

on the shaft 26, the dwells or high portions of the cam serving to hit the valve from its seat against the tension of the spring 30, which normally seats the valve,-and issu'tficicntly strong to prevent the valve opening under operating pressure.

Near the top of each cylinder, opposite the fuel inlet port, there is provided a chamber at, the upper edge of which forms a seat for a by-pass valve 35, carried by an elongated stem 36, which is suitably guided in bearings in the engine structure, said valve being normally held to its seat by a spring 37 as shown in Fig. 4, and being unseated by means of a cam 38 carried by the cam shaft 25, the raised portion or dwell of the cam being substantially 150 in extent so that the by-pass valve 35 is held open during 300 of rotation of the crank shaft 9. Each cam 38 is so adjusted on the shaft'26 that it opens the bypass valve 35 of the corresponding cylinder when the piston in the latter has moved downward on its power stroke a distance equal to approximately 60 of the crank throw, so that the by-pass valve of each cylinder relnainsopen until the corresponding piston reaches approximately its upper limit on each exhaust stroke. Connected to the bypass valve chamber 341- of each cylinder, and extending to, and .connectmg with the exhaust valve chamber 31 of a companion cylinder is a by-pass pipe or conduit which serves, on the one hand, to convey partof the expanding gases from a cylinder in which an explosion is taking place to the opposite end of a cylinder .01 cylinders, the pistons of which are about to begin their upward movements, and, on the other hand, serves to convey the burnt gases or products of combustion from a cylinder in which the piston is on its exhaust stroke, to the exhaust valve chamber of a companion cylinder or cylinders, whence said gases are ultimately exhausted into the exhaust mani fold 32. V

The particular disposition and arrangement ofthe by-pass conduits in the engine illustrated, are indicated in Figs. 2 and 9, said conduits being shown in full lines in the former figure, and by ingle dotted lines in the diagram represented by Fig. 9. Bypass pipe 0 leads from-chamber 34 of cy-lin der No. 1. to the exhaust valve chamber 31 opposite the lower end of cylinder No. 2, the lower end of the bypass pipe registering with an opening in the base flange immediately above the exhaust valve chamber Near its lower end, the by-pass pipe is connected with a branch 71 which communicates with the exhaust valve chamber 31 of cylinder No. 5, where it is joined by by-pass pipe 78, connecting valve chamber 34 of cylinder No. 6, with the exhaust valve chamber ofcvlinder No. 5. Similarly, a by-pass pipe 72 connects the by-pass chamber of cylinder No. 2, with the exhaust valve chamber of cylinder No. 3, and is connected by a cross-over 73 with the by-pass'pipe 77, which, in turn, connects theb y-pass valve chamber of cylinder No. 5 with the exhaust valve chamber of cylinder No. 4. "Pipe 74 likewise provides aby-pass from valve chamber 34 in cylinder No. 8 to the exhaust chamber'31 in cylinder No. 1 and is connected by a cross-over 75 with by -pass pipe 7 6 which connects valve chamber 34 ofchamber N0. 4, with the exhaust valve chamber 31 of cylinder No. 6.

It will be understood, of course, that the connection with the description of the operation of the engine as a whole. 7

Connected with each of the air compres sion spaces, in the lower enlarged sections of the several cylinders, is an outlet pipe 41 which delivers the air, compressed by the annular shoulder on the lower part of the piston,'into ZtHltLIllf'OlCl which extends across the engine, as illustrated in Figs. 1,

'3 and 9; Located in each cylinder wall at a pointjust above the lower limit of travel of 'the upper end of the piston 4 is a port 80, which isconnect-ed wit-h the manifold 40 by means of a'pipe 40. Each'of said pipes 41 is provided with suitable check valve 41 to prevent back pressure. .The purpose and function of the manifold 40 and the port 80 in each cylinder are the same as described in .my prior Patent No. 1,106,194, the, compressed air from the manifold 40 being admitted to each cylinder just before the upper end ofthe piston therein reaches the lowerrend of its suction stroke, to supply an excessof air to produce complete combustion of the fuel charge after the latter has been compressedand fired, and also serving to sweep out or scavenge the cylinder of the products of combustion'just beforethe pis ton reaches the end of its power stroke and during the first part of the exhaust stroke, as is'more fully explained in my prior patent aforesaid.

As indicated, the present invention also includes means for starting the engine,

either alone, or when coupled to the vehicle.

or other machine whichit is employed to drive. To effect this operat on, the manl- I fold 40, which receives air under pressure.

from the several cylinders, is connected by ableeder pipe 40, to a pressure tank 43,

which may be located at any convenient place adjacent the engine, said'bleeder pipe I being provided with a check valve 42 to prelet from the tank 43 is bywayof a valve 45 mounted in casing 44, secured to one end of the tank and coupled to a pipe 47, which,

in turn, is connected with a horizontal pipe 48, runmng longitudinally of the engine.

Branch conduits 49 from header pipe 48, connect thesame with air inlet valve chambers 55, formed in the engine casing adjacent the respective cylinders', each chamber 55"communicati1ig with the corresponding exhaust valve chamber 31, through an opening normallyclosed by a valve '50, as illustrated iniFig.-5, sothat, when a given valve 50 is opened, air under pressure from the tank'43 will be admitted to the corresponding exhaust valve chamber whence it isdistribu'ted under the'lower faceof the piston in the corresponding cylinder and to certain of the other cylinders of the engine to start the latter.

Each valve 50 is provided with a stem 52,

which is suitably guided for vertical recip rocation in bearings formed in the casing,-

and is normally held to its seat by a spring 53.. Thelower end of the valve stem 52 is engaged byan adjustable tappet 65 mounted upon a rod 64, the upper end of which is guided in bracket 67, projecting from the inner side of the engine frame. The lower end of rod 64 is connected to ears 68 formed upona sleeve 62, which, in turn, is rotat-ably mounted on an eccentric sleeve61'r1gidly se.

cured to a shaft 60 journalled in the ends of the engine casing below the crankshaft 26,the outer end of the shaft 60 being provided with a suitable means, such as a hand crank,a foot lever, or the like (not shown) for turning the shaft through 180. Upon the opposite end of each sleeve 62, is secured a rocker arm" 63, which is adapted to be moved into and out of the path of movement of a cam 66 fixed to the cam shaft 26.

Each cam 66 is provided with two opposite I operatingfaces or dwells, and each of said cams is fixed to the shaft in such relation that it. opens the air intake valve 50 just 'afterthe exhaust valve of the same cylinder s closed, and closes the said airintake valve ust before the corresponding exhaust valve 'opens. lVhenthe shaft 60 is turned in one direction, the eccentric sleeves61 withdraw the rock levers 63 from the path of movement ofthe cams 66 so'thatthe air intake valves are not operated. When, however, the shaft 60 is turned in the other direction,

the eccentric sleeves 61 raise the correspondingrock levers 63 into position' to be engaged by the high portions of the cams 66,

thereby causing each intakevalve 50 to be air intakevalves and operating mechanism vent back pressure from the tank. The out therefor, namely, cylinders Nos. 1, and 3,

but this particular disposition. and arrangementof the air intake valves is sutlicient to produce av sufiiciently powerful torque to start the engine from a position of rest, when air under pressure from tank s3 is admitted to the engine, as will bemore particularly described hereinafter.

Under ordinary circumstances, the air stored in the tank a3 is under the normal pressure nduced n the manifold as herev nbefore explained, and is snfiicient to start the engine alone, as the pressure can be readily maintained at fifteen pounds or more above atmosphere, wh ch, with a reasonable tank capacity, is ample to start-the average engine. Vhen, however, it is desired to startthe engine without coupling or disconnecting the same from the vehicle or other machine which it drives, anotherphase of the invention is brought into operation, namely, the self-braking effect of the mac hine,produced by closing the exhaust manifold 32by means of a three-way valve 3.2 therein, which is adapted to cut off the exhaust and divert the exhaust gases byway of a pipe 4E7 into the tank said pipe 47 being connected to the exhaust manifold 32 at apoint adjacent to said valve 3:) as illustrated in Fig. 9. This choking of the exhaust builds up a heavy back pressure, the several pistons in exhausting the spent gases from the respective ends of the cylinders exercising a pumping action to build up the back pressure in the exhaust manifold, which is sufiicient to bring the engine and the machine operated. thereby to a quick stop, but without heavy shocks or jars or undue strain on the engine parts, for, while the back pressure is built up in a relatively short time, the increase in the back pressure is in proportion to the speed of the engine, so that sudden choking or stopping of the latter is passed through theregular cycles when the en ine is turned over. It will therefore be that the back pressure as built up'in the exhaust man fold and the storage tank 43 is not only'elfective in braking the engine and vehicle, but is also immediately available for starting the engine and vehicle smoothly and evenly without necessitating the shifting of gears, clutches or ordinary 'brake'mechanisrn.

Vhile the engine illustrated in the drawings involves differential pistons, it isto be understood that the invention is not limited to this articular type ,of. apparatus, as pis laims directed to the same are to be given a correspondingly broad interpretation. The

invention, however, probably finds its best exemplification in an engine of the six-cyl nder type, such as illustrated. in which each ton which serves as an air compressor, as described, but, what is more important, affords a greatly increased or augmented surface on the lower face of each of the pistons and correspondingly increased cylinder volnme below the enlarged piston head, so that a practically complete expansion of the burning gases can be obtained and all of the heat generated thereby converted into ef fective work, sion of the exploding charge, which is'bypassed to the under side of the large ends of the piston. in predetermined order, and the pressure of the exhaust from the upper end of the cylinder in which the exhaust stroke taking place, will be effective in producing upward forces or pressures on various pistons which may be made to counterbalance the downward pressures of the other cylinders during the explosion strokes of the latter, so that the crank shaft will be practically free of vertical stresses and the resultant frictional losses will be obviated.

The operation of the apparatus as described is as follows. reference being had to the diagram inFigfS, and the cylinders fir- ,ing in the order, 1, l, 2, 6, 3, 5. Assume that the chargein cylinder No. 1 has been .fired and the piston of No. 1 cylinder has completedqa portion of its stroke represented by a rotation of the crank shaft. At this time, the valve 35 in cylinder No. 1 connecting with the by-pass is opened,permitting a part of the expanding gases above the piston in cylinder No. 1 to pass under the pistons in cylinders No. 2 and No. 5 which are at the lower limits of their strokes. The expanding gases therefore are exercising a downward thrust on the piston in cylinder No. l, which is continued to the lower limit of the piston travel, and upward pressure on the pistons in cylinders No. 2 and No. 5 which pressure is continued until these pistons reach their upper limits'of movement. The exhaust valve adjacent each of the cylinders is timed to open when the piston in the corresponding cylinder begins its downward travel and remains open during 180 of the crank throw. Therefore, it will be seen that the exhaust valve adjacylinder is provided with a differential pisand furthermore, the expancent cylinder No. 1 is open during the entire power stroke of the piston in said cylinder, and any pressure on the lower side of the pistonfin cylinder No. 1 is immediately relievedthrough the exhaust. Just before the piston in cylinder No. 1 reaches the lower limit of its stroke, ituncovers port 80 admitting air under pressure from the manifold .4LOready to scavenge the products of combustion from the cylinder above the piston. The piston in cylinder No. 1 is now ready to begin itsreturn stroke. This air under pressure also passes by wayof valve 35 in cylinder No. land by-pass pipes 70, and 71, under the pistons in cylinders No. 2

' and-No. 5, and this condition maintains until piston No. 1 begins its reverse movement. When the piston'in' cylinder No. 1 reaches the lower limit of its stroke, the exhaust valve adjacent said cylinder closes. It will be noted that the reverse movement of piston No. 1 is opposed by the air pressure admitted at port 80, but'this will be compensated by the upward pressure on the lower sides of the pistons in cylinders No. 2 and No. 5. As soon'as the piston in cylinder No. 1 closes the port 80 this air pressure is cut off. The continuation of the reverse movement of the piston in cylinder No. 1 forces the products of combustion and the scavenging air from the upper portion of the cylinder through the bypass valve 35 and builds up the pressure on the under sides of the pistons in cylinders No. 2 and No. 5, and when the latter pistons reach the upper limit oftheir movement, the exhaust valves associated with the corresponding cylinders are opened and the gasesin the cylinders below the pistons therein will be expelled when the pistons in No. 2 and No. 5 begin. their downward stroke. Mean while, the piston in No. 1 continues its upward movement, completing the exhausting and scavenging of the products of combustion and air in the upper part of the cylinder, until it reaches the upper limit of its stroke, the exhaust passing out through the exhaust valves adjacent the cylinders No. 2 and No. 5. Simultaneously with this operation, the pistons in Nos. 2 and 5 are continuing their downward movement and expelling the gases in the lower portions of the respective cylinders through the same exhaust ports. The piston in cylinder No. 1 is then readyfor its suction stroke and at this time, the exhaust valve adjacent cylinder No.

' 1 isopened and the by-pass valve 35 in cylinder No. 1 is closed. Immediately thereafter, the fuel intake valve 16 to cylinder.

No. 1 is opened and the piston in said cylinder begins its downward travel, the lower face of the piston forcing the air and products of combustion in the lower part of the cylinder through the exhaust port of said cylinder No. 1 past'the open exhaust valve therein. During the suction stroke of piston No.- 1, the intake valve remains open for 120 ofcrank travel and, when the upper end of the piston uncovers the port 80, air, under pressure from the manifold 10 rushes into the cylinder to provide an ex-' cess of air necessary to afford complete combustion of the fuel delivered through the intake valve from the usual form of carburetor or other charge-forming device. The port 80 remains open until it is closed by the piston when the latter has made part of its return or compression stroke, the co1n pression continuing until th'episton reaches the upper limit ofits stroke.

The charge is then fired and the series of operation, as described, is repeated in the usual and regular order of a four-cycle engine. The same cycle of operations is taken up and carried out by cylinders Nos. 1, 2, 6, 3. and 6 in sequence. By reference to the diagram in Fig. 10, it will be noted that cylinder No. 1 has'fired and has traveled a distance equal to 60 of crank throw, at which time the piston in cylinder No. 6, has traveled an equal distance on its suction stroke; -piston No. 5 is at the lower limit of its power stroke and has forced out the gases in the lower portion of its cylinder; the'piston in cylinder No. 2 is beginning its compression stroke; piston in cylinder No. 3 is begin-,

cylinders below the pistons are asfollows:

The piston in cylinder No. 1 is forcing the exhaust gases past theopen exhaustvalve 29 associated with said cylinder No. 1, a portion'ofthe expanding gases from the top of cylinder No. 1 is passing through by-pass pipes 70 and 71 under the pistons in cylinders Nos. 2 and 5 and develops an upward power stroke on the under faces of thepistons in these cylinders, thereby assisting the piston in cylinder No. 1 in driving the crank shaft and counterbalancing the vertical thrust on said shaft, so that thelatter practically fioatsin its bearings. Thelower portions of cylinders Nos. 3 and 4 are receiving the exhaust from the upper portions of cyl inder No. .5,.through the by-pass valve 35' and .the by-pass pipes 77 and 73 and as this exhaust pressure is augmented bythe scave ging airin the manifold 40, the lower as follows: Shaft 60 is rotated 180 to bring the lovers 63, carried by the sleeves 62 on theeccentrics 61, into the path or movement or" the cams (56 on the cam shaft 26, one cam 68 being provided for each of cylinders Nos. 1, 2 and 3-,fand having the cam faces thereon spaced to operate the air intake valve 50 of each cylinder inn'nediately after the exhaust valve of said cylinder is closed, which latter operation takes place when the piston in the coi'resphnding cylinder reaches its lower limit of trav l The air under pressure in tank 43 is ad 't-tedto pipe l? and manifold &8 by opera ing valve 45 by its operating handle d6, so that the pressure from the tank will be admitted to the manifold ready to be delivered to the cylinders in regular order: p v

Referring to the diagram in Fig. 9, it will be noted the. the pistons in cylinders Nos. 2 and 5 are at their lower limitsof moveme t and the pistons in Nos. 3 and 4- are I oaching the upper limit of their movem r t. so that thecam 66, corresponding to cylinders Nos. 2 and 5 will unseat air intake vali es' 50 corresponding to said cylinders nos. 2 and 5 when the cam shaft 60 is operated by hand to bring'the levers 63 up into en aging position. The air pressure in the manifold willthere'fore pass into the lower portion oi cylinder No. 2, thence by my-pass 71 to the lower portion of cylinder No. 5, and by-pass to the upper portion or cylinder No. l. The opening of air intake valve at the bottom of cylinder No. 3 admits the air presshre to the lower side of the pistons in N s. 3 and i, so that the air pressure is' operating to force piston No. 1 downward and pistonsllos, 2, 3', 4 and 5 upward. v This will be suiiicient to initiate the starting operation As the cams 66 have two operating sections, or dwells, at opposite points, and substantially in extent, each air intake valve will be opened immediately its corresponding piston begins its upward movement and willremain open during approximately the of crank throw. In other words, the valve 50 (it each cylinder will close just before the corresponding e);-

haust ve opens, and open just after the said feiznaust valve closes.

When the piston in cylinder No. 1 reaches the lower limit of its stroke and begins its upward movement, air intake valve 50 opens to admit airto the under side of the piston therein, and also to the upper side of the piston in cylinder No. 3, by way of b pass Til, thence by way of bypass sections Thhhd "T6 to the under side of piston in cylinder No. 6, which piston is beginning its upward stroke. At this time, the by-pass valve 35 in cylinder No. 4i is closed, so that the air will not interfere with the suction stroke of the piston in said cylinder No. l. It will thus be seen that the air pressure is admitted to the tops and bottoms of the several cylinders in regular order to produce a powerful torque on the crankshaft and start the engine. It will be notedthat the several by-pass valves andthe exhaust valves are operated in their regular order and sequence to maintain the proper tribution of the air pressure to the cylinders and to effect exhaust of the air after it has done its work, the latter being brought about by reason of the fact that the exhaust valves of the cylinders are opened immediately after the valves which supply the air pres; sure to the Corresponding cylinders are closed. It will be noted further that the air under compression used to start the en; gine does not interfere with the supply of fuel to the respective cylinders on thesuction strokes, as the by-pass valye of each cylinder is closed during the whole intake stroke so that the sta'rting'air pressure does not have access to a cylinder which is taking a fuel charge. p The air pressure hormally'b'uilt up inthe tank 43 is derived from the air which is compressed in the portion 8 of each ylinder on the upward stroke ofthe corresponding piston and is suflicie'nt to start the motor alone, because of the heavy preponderahce of the pressure on the under sides oi the pistons which are moving upward over and above thep'r'essure produced. in one or more of the cylinders in which the gas charge is being compressed as the areas of the lower portions of the pistons are greatly in e. :cess of the. upper portion thereof, as hereinbeiore described. I

t is also to be noted that the engine may be effectively employed to brake. a vehi- 'cl'c or i'ira'chihe which it is employed to drive, and thisv is accomplished by turning the valve 32 in the exhaust manifold to deliver the exhaust gases from all. offthe cyliiulers through the pipe 2L7, into the tank 43, the engine operating as ap'ump to. compress these gases to a relatively, highdegree, the back pressure. being eiiective to bring the engine -and the. machine driven thereby quickly ,to rest without unnecessary shocks oijars; The heavier pressure 'dt'fgas thus produced in the tank will be suiiicient to start, not only the engine, but theveliicle or other machine driven thereby without necessitating the shifting of "gears or clutches or brakes so that both thefengine and the machin'eniay be started quickly and smoothly by the simple manipulation of the shah (30 which controlsfthe operationfotthe air intake valves '50 associated with the first three cylinders.

What I claim is 1. an internal combustion engine, coniprising multiple double acting cylinders ahd a piston in each cylinder, each cylinder having'a valved fuel inletfatone end and a valved exhaust outlet at the opposite end, by-pass conduits each connecting the iio 2. An internal combustion engine, como prising multiple double acting differential cylinders and a differential piston in each cylinder, each cylinder having a valved fuel inlet at one end and a valved exhaust chamber at the opposite end, by-passing conduits, each connecting the upper portion of one cylinder with the lower portion of a companion cylinder, valves controlling said conduits, means for opening the respective bypass valves during the first part of the explosion cycle in the upper part of the corresponding cylinder, means for holding the exhaust valve of each cylinder open during the'e-xplosion cycle of said cylinder to provide an exhaust for the lower part of said cylinder and the upper part of a companion cylinder, and means for delivering air under pressure to the upper portion of each cylinder near the end of the suction stroke and during the first part of the exhaust stroke of the piston therein.

3. An internal combustion engine, compris ing multiple double acting cylinders and a piston in each cylinder, each cylinder having a valved fuel inlet at one end and a valved exhaust outlet at the opposite end, by-pass conduits each connecting the upper portion of one cylinder with the lower portion of a companion cylinder, valves controlling said conduits, means for opening the respective by-pass valves during the first part of the explosion cycle in the upperpart of the corresponding cylinder, means for holding the exhaust valve of each cylinder open during the explosion cycle of each cylinder, an exhaust manifold connected with the several cylinders, and means for closing the outlet of said manifold; whereby the several cylinders and pistons will operate as a pump to build up a back pressure to brake the engine. 7

4:. An internal combustion engine, comprising multiple double acting cylinders and a piston in each cylinder, each cylinder having a valved fuel inlet at one end and a valved exhaust outlet at the opposite end,

'by-pass conduits each connecting the upper portion of'one cylinder with the lower portion of a, companion cylinder, valves controlling said conduits, means for opening the respective by-pass valves during the first part of 'theexplosion cycle in the upper part of the corresponding cylinder, means for holding the exhaust valve of each cylinder open during the explosion cycle of each cylinder, an exhaust manifold connected with the several cylinders, a pressure tank connected with said manifold, and means for closing the outlet of said manifold and delivering the exhaust gases to said tank; whereby the several cylinders and pistons will operate as pumps to build up a back pressure in the manifold and tank to brake the engine. I

5. An internal combustion engine, comprising multiple double acting cylindersand a piston in each cylinder each cylinder having a valved fuel inlet at one end and a valved exhaust chamber at the opposite end, by-pass conduits each connecting the upper portion of one cylinder with the lower portion of a companion cylinder, valves controlling said conduits, means for opening the respective by-pass valves during the first part of the explosion cycle in the upperpart of the corresponding cylinder, means for holding the exhaust valve of each cylinder open during the explosion cycle of said cylinder, air inlet valves located in the exhaust valve chambers of certain of said cylinders, an exhaust manifold connected with the exhaust valve chambers of the several cylin ders, a pressure tank connected with the exhaust manifold and having connections with the exhaust valve chambers controlled by the air inlet valves, and manually adjusted means for operating the air inlet valves in proper sequence to admitpressure from the tank and distribute the same to the several cylinders to start the engine. I

6. An internal combustion engine, comprising multiple double acting difierential cylinders and a differential piston in each cylinder, the larger piston sections acting to compress air on the up strokes, a manifold to which said compressed air is delivered, by-pass conduits connecting the upper portion of each cylinder with the valves during the first part of the explosion cycle in the upper part of the corresponding cylinder, a valved exhaust chamber near the bottom of each cylinder, means for holding the exhaust valve of each cylinder open duringthe explosion cycle of said cylinder, a pressure tank connected withthe air manifold and with the exhaust chambers of each I cylinder, air inlet valves in said exhaust chambers, and means for opening the inlet valves in proper sequence to admit pressure from the tank and distribute the same to the several cylinders to startthe engine.

In testimony whereof I affix my signa ture. I

i-innMoN E. DUNHAM. 

